Hydrophobic substrates, such as polyester, polyamide or polystyrene film bases and resin-coated paper supports, are well known commercial materials which possess a number of advantages for many uses. In the photographic industry, for example, such substrates are used as supports for various radiation-sensitive elements. However, the use of such hydrophobic materials in the photographic and other arts has been hampered to some extent because of the difficulty of suitably adhering various other layers to them, particularly when such other layers are hydrophilic in nature.
In order to improve the adhesion of various layers to hydrophobic supports, it is known to apply one or more intermediate layers to the supports before other layers are applied as described, for example, in U.S. Pat. No. 4,123,278 (issued Oct. 31, 1978 to Van Paesschen et al). Such intermediate layers are generally known as "subbing" layers and can include a wide variety of natural or synthetic resinous materials, adhesion promotors and the like.
During the manufacture of radiation-sensitive elements, but prior to applying radiation-sensitive or other hydrophilic layers to a subbed hydrophobic support, the support web itself is subjected to considerable mechanical handling over rollers and other web-guiding means. As a result, a considerable buildup in electrostatic charge occurs on the support web. Because of the insulative nature of the support material, little of this charge is dissipated by the time it reaches subsequent coating operations. Consequently, such electrostatic charge often interferes with coating operations and causes nonuniformities, streaks and other defects in the applied coatings. Further, during the coating of radiation-sensitive materials, the electrostatic charge often arcs or discharges thereby "fogging" the radiation-sensitive layers. Fogging shows up as small white dots in any image provided in such layers.
Attempts have been made to prevent or reduce electrostatic charge buildup either by making the support conductive or by coating the support with conductive compositions as noted, for example, in U.S. Pat. No. 1,981,425 (issued Nov. 20, 1934 to McNally) and in the Van Paesschen et al patent mentioned hereinabove.
However, such attempts have had limited success. While reducing electrostatic charge buildup to some extent, known conductive layers generally exhibit limited conductivity thereby reducing such buildup to an insufficient degree. Other conductive layers exhibit inadequate adhesion to hydrophobic supports. In particular, it has been difficult for workers in the photographic art to find coating compositions which, when coated and dried, will prevent or reduce electrostatic charge buildup. It has also been difficult to find coating compositions for use in forming conductive layers which readily adhere to hydrophobic supports.
Hence, there is a need in the art for a coating composition which is useful for providing conductive and highly-adherent layers on hydrophobic support materials.